Tempered glass sheet or plate



March 12, 1963 A. DO HUU CHAN ETAL 3,081,209

TEMPERED GLASS SHEET OR PLATE Original Filed June 10, 1952 3Sheets-Sheet 1 LII 2 LN w.

m ON ATTORNEY March 12, 1963 A. DO HUU CHAN ETAL 3,081,209

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TEMPERED GLASS SHEET 0R PLATE Original Filed June 10. 1952 3Sheets-Sheet 3 IN VENTORS.

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United States Patent 3,081,209 TEMPERED GLASS SHEET 0R PLATE Andre .DoHun Chan, Welkenraedt, Belgium, and Roger- Emile Lambert, Paris, France,assignors to Compagnie de Saint-Gobain, Paris, France Originalapplication Junelt), 1952, Ser. No. 292,704, now Patent No. 2,910,807,dated Nov. 3, 1959. Divided and this application July 27, 1959, Ser. No.840,214 Claims priority, application France June 15, 1951 v 3 Claims.(Cl. 154-57) The present invention concerns generally, the manufactureof objects of tempered glass, i.e. of objects of glass in which a stateof stresses (compressions and ten sions) is set up by heating theseobjects to a temperature approaching softening and then subjecting themimmediately to rapid cooling or chilling. Such objects have, as is wellknown, remarkable mechanical properties.

In particular, when glass windows and Windshields of vehicles areinvolved, the glass tempered under the recited conditions, ischaracterized in the case of shock, by being very strong and, if it doesbreak, will shatter into small fragments harmless to the occupants ofthe vehicle. This particular fragmentation, which is a safety factoroffered by this type of window, can, however, if it is very fine,produce an unfavorable change in visibility at the moment it shatters orbreaks into fragments.

To remedy this drawback attempts have been in the past to make glasswindows and Windshields in which certain areas remain untempered or ofless temper than the remaining area, so that in the case the whole sheetbreaks, the untempered or less tempered areas are not shattered infragments or are shattered in relatively large pieces and leave enoughvisibility for the driver.

It also has been suggested to subject the parts to be reserved and thezones around them, to a different thermal treatment in order to producea more energetic temper in those parts which are termed herein environalzones than in the parts to be reserved. However, the products obtainedso far by this process are not always stable and are apt to show acertain sensitivity to shock and considerably lower resistance withrespect to that of a product tempered in uniform manner.

Applicants have established that the instability is due 'to the factthat the stresses which arise from the difference in thermal treatmentbetween the reserved parts and the environal zones are susceptible ofstressing the reserved parts in tension. Now, it is known that when theglass is not tempered at all or only a little, as in the reserved part,it resists with difficulty to such tensile stresses.

temperature of the environal zone, as a result of which each reservedpart is compressed by the environal zone acting in the manner of a hoopor ring or at least is not subjected to tensile stresses by the portionconstituting the environal zone.

In this case, no stress, and in particular, no tension can developbetween the reserved part and the environal zone, up to the moment ofsolidification of the environal zone, since it is still in the plasticstate. On the other hand, from this moment and up to complete cooling,the reserved part, which starts cooling from a much lower initialtemperature than the environal zone and therefore contracts less thanthe other, can exert no tensile stress on the said zone, but on thecontrary is compressed by the latter acting in the manner of a hoop. If,while bearing in mind the tempering requirements for the environal zone,the operation is eifectuated in the limiting conditions consisting ofsolidifying at the same instant of the reserved part and the environalzone, both experience the same temperature drop and consequently returnto ambient temperature without one exerting any tension on the other.

Different modes of realizing the process of the invention can beemployed by differentiating the treatment of the reserved parts withrespect to the environal zones, either during the heating period or thecooling period, or during both.

Thus, for example, the heating of the reserved part can be moderated sothat its temperature at the end of the heating period is lower than thetemperature of the environal zone which is raised to a temperature closeto that of softening, sufiicient for it to take the temper. It is to beunderstood that the difference of temperature between the reserved partand the environal zone must be sufficient so that, in the course of thesubsequent cooling, the glass of the reserved part be at a temperaturelower or at most equal to that of the environal zone at the moment wherethis environal zone solidifies in its whole thickness. In this case, theheating of the reserved part may be sufficiently moderated so that, atthe end of the heating period, the temperature of the reserved part belower than the solidification temperature. (The term solidificationpoint or temperature as used herein refers .to the point or temperatureat which the glass is hard enough to support stresses for long periodsof time without plastic deformation. This temperature is also referredto as the strain point or temperature at which the glass viscosity is4x110 poises.)

It is also possible to carry out the heating operation in such a mannerthat, at the end of the heating operation, the reserved part be at atemperature higher than the solidification temperature. The advantage ofthis second method is that, at the beginning of the cooling, thereserved part, being at a temperature higher than the solidificationtemperature, is still plastic and is liable to yield in a certainmeasure to the temporary strains developed at this time in thesuperficial layers of the glass.

Consequently the risks of breakage which may result from these strainsis practically avoided. The cooling following the heating operation maybe uniform over the entire surface of the glass.

By way of contrast, the reserved part and the environal zone can beheated uniformly and raised to a temperature near to softening and theircooling differentiated. In that event the reserved part must be cooledin advance so that it solidifies before the environal zone, the

cooling of the reserved part during solidifying being nevertheless slowenough so that this zone be not or slightly tempered while thesubsequent cooling or chilling of the environal zone is rapid enough totemper this zone. In this case, there is obtained the same advantagethen in the preceding, the reserved part being at the beginning of thecooling operation at a temperature higher than the the heating period,succeeds in keeping the part to be reserved, cool enough with respect tothe environal zone,

so that during the cooling period which follows the heat-i ing, and atthe moment where the environal zone solidifies, the temperature of thereserved part is below or, at the most, equal to the temperature ofsolidification. Moreover, the presence of the screen during cooling, bymoderating the cooling effect on the reserved part at the moment ofsolidifying, makes it possible to obtain a reserved part that is not oronly slightly tempered.

If it is assumed that the temperature of solidification of the glassinvolved, is approximately 450 C., a screen can be so chosen that itsprotective power and its time of action during heating is sufficient tokeep the part to be reserved at a temperature of about 450 C., While therest of the sheet is raised to approximately its softening temperature,650700 C., for example. The temperatures herein given as examples arethose approximating if not identical with temperatures usually accordedsoda lime glasses. A slight increase in temperature, from 450 to 500 C.,is permissible for the reserved part on account of the cooling which itmay undergo, in spite of the screen, between the end of the heatingperiod and the moment where the intense cooling or chilling solidifiesthe environal zone. Further, this increase of tempera ture can begreater in case it is desired to have at the end of the heating period,the reserved part at a temperature higher than the solidificationtemperature.

To realize the desired difference in temperatures, the screen can beplaced from the start of the heating period over the part to bereserved, but then certain precautions must be taken to avoid breakageof the glass at the start of heating, for example, by controlling theheating according to a sufiiciently slow rate. Applicants have been ableto apply very rapid heating means in making tempered glass of the typeinvolved, by taking the precaution of inserting the screen duringheating only after a certain lapse of time during which the sheet ofglass is evenly heated without screening. As in an electric radiationfurnace where the normal time of heating of a sheet of glass is about 4minutes, applicants have been able, without danger of breakage, tointroduce the screen after 1 minute of heating, and let it remain duringthe last three minutes of heating.

In this instance the applicants used a screen completely opaque to heatrays, such as an asbestos plate, for example. During the three minutesduring which the sheet, with exception of the reserved part, could beraised to a temperature of 65'0" C., the reserved part is not raised toa temperature above that of 450 to 500 C., necessary for having thisreserved part at 450 C., at the moment of solidification of theenvironal zone.

But in order that the article, namely a glass sheet, should not bewarped by the thermal treatment which forms the present invention, theapplicants have verified that it is advantageous to use the screenduring the heating period, only after a uniform heating as long aspossible, i.e. after the heating without any screen. It is alwaysunderstood that the reserved part, during the cooling, reaches atemperature lower or at most equal to the temperature of the environalZone when said zone solidifies throughout its thickness.

The applicants have ascertained that this result may be reached bycontrolling the characteristics of the screen and its use by increasingits thermal efiiciency. Thus, the different following methods havesuccessfully been aplic p Tl 'lick metal screens are used, for instancemm. thick or more, which have thus a great absorbing capacity for heatwhich enables them to stay in the heating furnace during the heatingperiod, Without their temperature exceeding 400 C., for example, whilstglass that is freely exposed to the heat of the furnace reaches 650 to700 C. during the same time.

During the period comprised between two successive placings of thescreen on the glass sheet, the screen is cooled outside the furnace.

If the screen should stay in the heating furnace before being placed onthe glass sheet during the heating period, within said furnace isprovided a housing with heat insulating walls for lodging the screenbefore it is brought on the glass sheet. The insulating walls of saidhousing shelter the screen against the direct radiation of the heatingmembers of the furnace, for example, against radiation from electricalresistances.

The screen is shaped as a hollow plate and a cooling fluid such as airpasses therein for its cooling, either during its stay in the heatingfurnace, or also when it is applied on the glass surface.

When a housing is provided in the furnace for sheltering the screenbefore carrying it on the glass sheet, the walls of said housing mayalso be made of hollow metal walls wherein a cooling fluid, such as air,may be passed.

With such means used separately, or in combination, on example for theabove case where the heating period for the usual tempering lasts 4minutes, the applicants could carry the screen on the glass sheet only 3minutes after the heating begins, i.e. to put it into action only duringthe last minute, thus enabling to keep the initial planimetry of thisglass sheet unchanged.

Another operational method consists in starting with previously temperedglass. Applicants have in fact, verified that the previously temperedstate prevents the glass from breaking at the start of heating so thatsuch glass fitted initially with a screen, can be placed in a quickheating furnace.

According to a special mode of realisation of the present invention, theuntempered or slightly tempered reserved part which, as said, issurrounded by the so-called environal zone, tempered, which binds it,can have the form of a closed continuous band in the form of a ring orannulus and surrounding a tempered central area. As the previouslydescribed versions, this product is obtained by regulating the heatingand/ or coolmg conditions of the temper in such a way that the ring tobe reserved is at a temperature lower or, at most, equal to that of theenvironal zone at the moment when the latter solidifies. Of course, thesolidification of the environal zone and of the central area bounded bythe ring must be rapid enough to cause their temper, while the coolingof the reserved annular part must be manipulated in such a Way that itis not or only slightly tempered.

By way of example, the following description concerns a mode ofrealization of the invention in the case of a sheet of glass, whichconsists in regulating the temperature of the part to be reserved byplacing a screen close to or against each side of the sheet duringheating.

This application is a division of original application Serial No.292,704, filed June 10, 1952, now Patent No. 2,910,807, issued November3, 1959.

FIG. 1 represents the heating and cooling apparatus in side view with apart of the furnace broken away.

FIG. 2 is a vertical section view of the heating furnace along the linelI-II of FIG. 1.

FIG. 3 is a detail, in vertical section, along the line III III of FIG.1.

FIGS. 4, 5, 6, 7, 8 and 9 represent various types of screens intransverse section and elevation.

'FIG. 8a is a modified form of the screen represented in FIG. 8.

FIG. 10 is a side view representing the appearance of a sheet of glasshaving been submitted to a treatment according to the invention andwhich was broken by shock in the environal zone.

FIGS. 11, "12, 13 and 14 represent, in vertical sections and front viewstypes of screens which are particularly apt to avoid the deformation ofthe glass sheet during the thermal treatment according to the invention.

FIG. 15 is a vertical view of an arrangement for placing the screen inrelation to the glass sheet.

The sheets of glass 1 suspended normally as usual from two small chains2 terminating in clamps 3 are moved -gion of the sheet. ing the finalperiod of heating (position C) and so prohorizon-tally in the furnace 4according to the arrow 1. The design represents three positions A-B-Cwhich each sheet occupies successively during the process of heating. Atthe furnace exit is the cooling or chilling apparatus 5 inside of whicheach sheet takes its place after heating.

To assure the travel of the sheet, the rod 6, to which are attached thesmall chains 2, may be an associated part of a carriage which, throughrollers 7, rolls over a horizontal rail 8 supported by brackets 9mounted on the furnace or in any other suitable way. A screen consistingof two symmetrical pants 10a and 10b serves to mask the part of thesheet of glass that is to be untempered or slightly tempered. Theexample in question refers to the treatment of a sheet which, originallywas glass normally annealed. In this case, the screen masks the glassonly after a certain period of heating, the part which is to have lesstemper or no temper being then, during this period, heated the same wayas the remainder of the sheet. This period is, in the examplerepresented, that of the location of the sheet at position A. Duringthis period, the screen Uta-10b is kept away from the sheet, althoughinside the furnace, where, in consequence, it is heated itself.

After the sheet has remained at position A for a period approximatelyequal to a third of its total stay in the furtrace, it is moved toposition B. By a device described later, the screen is then lowered tomask the desired re- The screen remains then in place durtects the zoneagainst the heat within and radiation of the furnace, so that on leavingit, the said region is not as hot as the rest of the sheet.

At the moment the sheet is placed in the cooling apparatus 5, itstemperature is much lower in the part that is to remain untempered orslightly tempered, than in the environal zone. In the example underdiscussion, the screen remains in place during the rapid cooling orchilling, which may be accomplished by any convenient means, such asjets of air projected onto the sheet from nozzles 11 fitted in tanks fedby compressed air. The screen plays then an insulating part against theeffect of the cooling jets and since it is integral with the carriagewhich supports the sheet and independent of the blowing tanks, thelatter may be given any desired motion of displacement parallel to theplane of the sheet, for example, a circular motion by means ofeccentrics 13 rotating about axes 14, while the blowing is excluded fromthe part bounded or masked by the screens.

The lowering of the screen 19a-10b on the sheet such as anticipated whenit occupies position B, is facilitated by a device represented in detailin FIGS. 2 and 3. A handle .15 turning about an axis 16 supported by thecarriage beam 6 is equipped at its lower end with a hook 17 from whichthe screen holder 18 is suspended by means of a rod 19. Pushing the endof handle which emerges on the outside of the furnace causes theunhooking of the screen holder, which then drops and lodges close to oragainst the sheet of glass. In this descent the screen holder is guidedby metal pieces between which the ends of bar 19 passes. The bottom partof pieces 20 serves further as stop of the downward motion as represented in FIG. 2.

The screens utilized can be of insulating material such as asbestos, orconductive material such as metal (steel, brass, etc.) or a combinationof such materials. It will be of advantage to select a material or acombination of materials such that the screen is able to pass throughthe cycle of successive heating and cooling of manufacturing inquantities by sensibly resuming the same temperature for each heatingand cooling so as to assure constantly the same thermic protection.

The shape of the screens is preferably that of a cover or lid, the edgesof which, by resting against the sheet of glass during treatment, keepthe interior portions or main area at a proper distance to assure thedesired protection. It may be of interest to give the screen anonuniform thickness to obtain controllable effects of intermediarytemper between complete absence of temper and appreciable temper. Inparticular, applicants have obtained satisfactory results by usingscreens such as represented in FIGS. 4 and 5 (section and elevation) and6 and 7 according to which the screen is made of metal plate of whichthe center is of a greater thickness 22, 'or lesser thickness 23, thanthe annular part 2.4. Of course, if the reserved part of the glasssheet, i.e., untempered or slightly tempered part is to have the form ofa circle, the screen must have a shape corresponding to it. For example,if the band is to have a circular shape, the screen should have theshape of an annulus or ring of suitable width, such as shown in FIGS. 8and 9, in which the screen has a cavity 25 in the center to let the heatwithin the furnace as well as the cooling air blasts reach the glass, toform an islet of tempered glass centrally of the ring or annulus ofuntempered or slightly tempered glass.

It has been found that the opening 25 can be fitted advantageously witha sieve, wire mesh, perforated plate or similar device 25a, as shown inFIG. 8a capable of letting only a portion of the heat within the furnacethrough as well as a portion of the cooling air. In the product thusobtained the central block or islet presents a certain mechanicalresistance due to partial temper, but shatters in case of breakage inpieces large enough to assure sufficient visibility. j

FIG. 10 shows'the fracture of tempered glass with a part reservedaccording to the invention. It is seen that the lines of fracture of theglass in the environal zone which are directed toward the center of thereserved part,

' start an inflexion by arriving in its vicinity and stop withoutentering the reserved part, which is explained by the fact that the saidpart is in the state of compression. Bordering the reserved part, theglass shows the same type of breakage, characteristic of safety temper,as in the rest of the environal zone.

In FIGURES 11 and 12, the screen is made of a single metal sheet 26having a cavity 25. The metal sheet 26 is maintained at a fixed distancefrom the surface of the glass sheet by the rigid rods 27 and the spacingmembers or nogs 28 which are integral with the rigid rods 27 and whichare preferably copper and thin members.

The applicants have found in fact that it is advantageous to provide acertain gap between the outer edge 29 of the screen and the glass sheet,at least during the cooling period by blowing. Such arrangement enablesthe reserved part and, in particular its outer edge, to cool between thebeginning of the blowing and the moment the environal zone solidifies.Thus, as above explained, the temperature of the glass in the reservedpart when blowing begins, may be higher than the solidificationtemperature.

Besides the mode of keeping the screen at the correct distance from theglass sheet by means of thin nogs made of copper (or of any very goodconducting metal) has been verified as bringing no risk of breakageduring the changes in temperature involved in the method according theinvention and this mode of keeping is a part of the invention.

In FIGS. 13 and 14 the screen 30 is hollow and is kept in position bypipes 31 and 32 which also are used as inlet and outlet pipes for acooling fluid, such as air, which circulates according to the pathindicated by arrows.

FIG. 15 represents an example of applying the method to a windshield formotorcar. In that windshield, the part to be reserved is placed not inthe middle, but near one end, opposite the drivers seat. Very often,windshields are tempered in vertical position as illustrated by FIG. 15,the glass sheet being suspended from the clamps 33 as in known manner.In that case, the applicants have verified that it is advantageous toput the reserved 7 part 34 at the lower part of the glass sheet asillustrated by FIG. 15, the screen 35 passing from the waiting position35a to the position 3511 at the place of the part to be reserved. '36represents the heating furnace. The advantages of this arrangement arethe following ones.

It is known that in the process according to the invention, the zonewhich environs the reserved part shrinks during the cooling andcompresses it in the manner of a hoop. Reciprocally, said environal zoneis submitted to a tensile stress which corresponds to the compressivestress that it exerts. If the reserved part is at the top of the glasssheet suspended at one of its small sides, the zone, that environs thereserved part and acts as a hoop, is submitted not only to said tensilestress, but also to the weight of the lower part of the glass sheet andthe risk of breakage during the process is increased. On the contrary,this risk of breakage is suppressed practically when the glass sheet isplaced, according to the present invention, so that the reserved part isat the bottom of the sheet and the weight of the lower part of saidsheet below the reserved part has a relatively low value.

In the application of the invention described it Was taken intoconsideration that the sheet of glass could have more than one reservedzone (disk or circle) without difiiculty or fundamental modification ofthe equipment; the invention includes the realization in which the sheetof glass has several zones answering every desirable relativearrangement.

It also is self-evident that the above described invention in itsapplication to a sheet of glass used as window of a vehicle applies toall types of glass, in order to obtain for example in tempering blocks,insulators, structural glass, etc., parts which are of less temper thanthe rest of the glass object and which, nevertheless, do not lower thestrength and stability of the object.

We claim:

'1. A new article of manufacture comprising a glass sheet having ahighly tempered outer environal zone, a partially tempered inner isletwithin said environal zone, and a predetermined reserved zonesubstantially free of temper, having the shape of a continuous bandclosed on itself and disposed between said inner islet and outerenvironal zone.

2. A new article of manufacture comprising a glass sheet having a highlytempered outer environal zone, an inner islet within said environal zoneless tempered than said environal zone, and a predetermined annularreserved zone surrounding said inner islet and located between saidouter environal zone and inner islet and having a degree of temper lessthan that of said islet, so that the degree of temper of said islet isintermediate that of the environal zone and the annular reserved zone.

3. An article as set forth in claim 2 wherein said annular zone iscompressed by the outer environal highly tempered zone acting as a hoop.

References Cited in the file of this patent UNITED STATES PATENTS2,009,748 Sherwood July 30, 1935 2,177,324 Long Oct. 24, 1939 2,244,715Long June 10, 1941 2,418,713 Holmes et a1. Apr. 8, 1947 2,762,166 VentSept. 11, 1956 FOREIGN PATENTS 826,690 France Jan. 12, 1938 606,756Great Britain Aug. 19, 1948 609,921 Great Britain Oct. 8, 1948

1. A NEW ARTICLE OF MANUFACTURE COMPRISING A GLASS SHEET HAVING A HIGHLYTEMPERED OUTER ENVIRONAL ZONE, A PARTIALLY TEMPERED INNER ISLET WITHINSAID ENVIRONAL ZONE, AND A PREDETERMINED RESERVED ZONE SUBSTANTIALLYFREE OF TEMPER, HAVING THE SHAPE OF A CONTINUOUS BAND CLOSED ON ITSELFAND DISPOSED BETWEEN SAID INNER ISLET AND OUTER ENVIRONAL ZONE.